#include "stdio.h"
/*
int main ()
{
 int i,j,flag;
  for(i=1;i<=100;i++)
     { 
      flag = 1;
	 for(j=2;j<i;j++)
    {
       if (i % j == 0) 
       {  
          flag=0;
           break;
       }
    }
       if(flag == 1) 
       printf("%d,",i ); 
    }
}*/

int f8(int x)
{
   int i = 0;
   int sum = 0;
if (x == 1)
{
   return 1;
   }
else 
{
   sum = f8(x - 1) + x;
}
return sum;

}
int main ()
{
   int m;
   int t;
   scanf ("%d",&m);
   t = f8(m);
   printf ("%d",t);

}